Glugging kitchen sink

[Caws]

Our sink has started making a glugging noise when you put water down it. I've checked all pipes including the overflow and they're clear. I've used Mr Muscle drain unblocker and a foamer down there and still it bloody glugs!
The only place I haven't checked is the pipes outside the house but I don't know how they're fitted. They look like push pipes but they're stuck solid and I daren't force them.
It's driving me mad.
Has anyone got any ideas what I can try next?

 

[terryplumb]

Have a look outside where the waste pipe ends. Does it go into a vertical soil stack or down into the floor ,to a grid ? If it's the latter ,is the end of the pipe submerged in water ?

 

[Caws]

It goes into a drain. Not submerged in water (although that did happen a few months ago when the drain blocked with food and that caused glugging). Drain is all clear now. It's baffling especially as it's only started this week.

 

[terryplumb]

Can you post pics of pipe outside and it's end / drain ?

 

[Caws]

Will try now.

 

[Caws]

 

[Caws]

 

[Caws]

Rubbish photos I'm afraid. It's gone dark outside

 

[terryplumb]

That looks like a long pipe run ,and I can't see the end of the pipe. Is it definitely open to the atmosphere ,fill the sink and then pull the plug out and go outside and see if the end of the pipe has water backing up.

 

[terryplumb]

There are two pipes entering the horizontal pipe , probably sink and an appliance ( washing machine maybe).which one is the sink ? I assume it's the higher one at the right side, the short section of pipe from the far right to the second inlet APPEARS to not have a continuous downward fall ,is that so ,or is the picture decieving ?

 

[Caws]

Just checked the water - all flowing freely. The higher pipe on the right is the washing machine, the lower one the sink. The angle of the photo is crap but the whole length of pipe has a downward slope. We've been here for a few years and the only time I've had this glugging before was when the drain was blocked. It's really odd. I wondered if there is a partial blockage on those pipes outside but then the water seems to be flowing freely. It's certainly a mystery as to why it's just started now.

 

[Caws]

My family say I'm fussing over nothing but it's bugging the hell out of me. Is it harmless or could it indicate a bigger problem somewhere?

 

[terryplumb]

It looks like the pipe run is partially restricted . So it's internal diameter is reduced somewhere ,that results in the water creating suction behind it as it flows thru the pipe ,hence the glugging sound at the sink .

 

[Caws]

Does that mean a blockage?

 

[terryplumb]

Partially. I assume you hear the same glugging when washing machine pumps water out ?